A power-generation system using a conventional fuel cell is described below by referring to FIG. 9.
In FIG. 9, symbol 1 denotes a fuel cell and a fuel treater 2 water-vapor-reforms a material such as a natural gas, generates a gas mainly containing hydrogen, and supplies the gas to the fuel cell 1. The fuel treater 2 is provided with a reformer 3 of generating a reformed gas and a carbon-monoxide shifter 4 of making carbon monoxide react with water to produce carbon dioxide and hydrogen. A fuel-side humidifier 5 humidifies a fuel gas to be supplied to the fuel cell 1. Symbol 6 denotes an air feeder that supplies air serving as an oxidant to the fuel cell 1. In this case, an oxidation-side humidifier 7 humidifies supplied air. Moreover, the power-generation system is provided with a cooling pipe 8 of supplying water to the fuel cell 1 to cool it and a pump 9 of circulating the water in the cooling pipe 8.
Moreover, when generating power, the exhaust heat due to the power generation in the fuel cell 1 recovers in a hot-water storage tank 13 via an exhaust-heat recovery pipe 12 by a heat exchanger 10 and a circulating pump 11 under the connection of the system.
When generating power by the above system, the fuel treater 2 requires water in order to water-vapor-reform a material such as a natural gas by the reformer 3 and moreover make the carbon monoxide contained in the reformed gas react with water by means of the carbon-monoxide shifter 4 to produce carbon dioxide and hydrogen, the fuel-side humidifier 5 requires water to humidify a fuel gas to be supplied to the fuel cell 1, and the oxidation-side humidifier 7 requires water in order to humidify supplied air. The water required for the above power generation has been supplied as city water or ion exchange water from the outside.
However, the above conventional configuration has a problem that a reformation catalyst or shift catalyst stored in the reformer 3 or carbon-monoxide shifter 4 of the fuel treater 2 is deteriorated due to chlorine ions or metallic ions eluted from a pipeline when using general water such as city water in the fuel-gas pipeline or oxidant-gas pipeline of the fuel cell 1, or a fuel gas or oxidant gas is ionized and electric conductivity is raised to cause a trouble in power generation by the fuel cell.
Moreover, when providing ion removal means such as an ion exchange resin in order to remove chlorine ions of general water such as city water or metallic ions eluted from a pipeline for a fuel-gas supply system or oxidant-gas supply system, there is a problem that regular maintenance of the ion removal means is necessary to secure the ion-removing capacity in accordance with an operation time, the ion removal means must be regularly replaced, or large ion removal means must be used in order to reduce the frequency of regular replacement.
Moreover, a power-generation system using a conventional fuel cell has the following disadvantages.
That is, to complete the power generation by the fuel cell 1, generally the system stops supply of a power-generation material to a fuel generator 2 and at the same time, supplies an inert gas such as nitrogen to the fuel generator 2 and circulation channels of a material gas and fuel gas of the fuel cell 1 and exhausts a combustible gas from the fuel-cell power-generation system.
Moreover, because the fuel cell 1 stops generating heat simultaneously when power generation stops, the cooling-water pump 9 and city-water pump 11 stop their carrying operations and circulation of cooling water and city water stops.
In the case of the above fuel-cell power-generation system, after power generation has completed, an inert gas such as nitrogen coming out of the fuel generator 2 at approx. 700° C. through the circulation channel of a fuel gas passes through the fuel cell 1 and is exhausted to the outside from the fuel cell 1.
In this case, however, the fuel gas remaining in the fuel generator 2 and the circulation channel passes through the fuel cell 1 by being pushed by the inert gas while almost keeping its temperature and is exhausted to the outside. Therefore, it is estimated that the inside of the fuel cell 1 has a higher temperature at only a part through which this fuel gas passes.
At the time of using the polymer electrolyte type for the fuel cell 1, it is necessary that a polymer electrolyte film used for an electrolyte is wet. However, when an inert gas which has a high-temperature but which is not humidified flows nearby the polymer electrolyte film, the polymer electrolyte film is locally dried to cause the power-generation efficiency of the fuel cell 1 to extremely deteriorate.
Then, even if the fuel cell 1 stops power generation, it keeps a temperature of approx. 70° C. for a while. Because the temperature is higher than an environmental temperature and the heat retained by the fuel cell 1 is only exhausted to the outside after circulation of cooling water is stopped. Therefore, it is necessary to use the heat of the fuel cell 1 also after power generation in order to effectively use the heat produced for the power generation.